Herron et al U.S. Pat. No. 5,137,537 is directed to absorbent structures comprising individualized, crosslinked cellulosic fibers having between about 0.5 and 10.0 mole % of a C.sub.2 -C.sub.9 polycarboxylic acid crosslinking agent, calculated on a cellulose anhydroglucose molar basis, reacted with said fibers in an intrafiber ester crosslink bond form, wherein said crosslinked fibers have a water retention value of about 25 to about 60. The Herron et al invention has preferred application for high density (above 0.15 g/cc) absorbent products, e.g., thin disposable diapers, feminine hygiene napkins and adult incontinence products.
The preferred methods of fiber preparation in Herron et al involve dry curing, i.e., curing aqueous polycarboxylic acid fiber admixture of at least 60% consistency.
One dry curing method described in Herron et al comprises contacting uncrosslinked fibers in unrestrained form with aqueous crosslinking composition so as to obtain uniform penetration and distribution of crosslinking composition thereon, dewatering, optionally drying further, defibrating the fibers into substantially individual form, optionally drying further without disturbing the separation of fibers into individual form obtained by defibrating, curing to cause crosslinking to occur, and optionally washing or bleaching and washing.
In a second dry curing method described in Herron et al, processing is carried out as described in the above paragraph except that either before or after being contacted with the aqueous crosslinking composition, the fibers are provided in sheet form and while in sheet form are dried and cured and the cured fibers are defibrated into substantially individual form.
Consideration has been given to obtaining C.sub.2 -C.sub.9 polycarboxylic acid crosslinked fibers while minimizing the cost of their production. Eliminating washing or bleaching and washing after curing reduces processing and equipment costs but also reduces the wet responsiveness of the absorbent product. Furthermore, reducing the amount of defibrating prior to curing reduces processing and equipment costs but also causes reduction in wet responsiveness and reduction in dry resiliency in the absorbent product and causes an increase in formation of balls of fibers which provide an appearance concern for the absorbent product.